You would have thought that if the Master Chief was not in Halo Reach they would have just said NO.

Instead they didn't and thus continued to build expectations that 117 will be in Reach. They will know the effects of saying stuff like this in an interview - if the Chief was not in Reach then Bungie would be crucified by the Halo community for allowing expectations to be built by not confirming the Chief was not in Reach. If that made sense!